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Initialization.md

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Initialization Parameters for PHM 2012 Dataset

Overview

This document describes the initialization parameters in backend/initialization.py that have been adapted for the PHM IEEE 2012 Data Challenge dataset from the PRONOSTIA experimental platform.

Dataset Characteristics

Parameter Value Description
Sampling Frequency 25.6 kHz (25600 Hz) Original sampling rate
File Duration 0.1 seconds Each CSV file
Data Points 2560 points Per file
Bearing Type SKF NKRF 25/20 PRONOSTIA platform
Rolling Elements (Nb) 13 Number of balls
Pitch Diameter (D) 34 mm Ball center circle diameter
Ball Diameter (d) 6.7 mm Single ball diameter
Contact Angle 0° Deep groove ball bearing

Working Conditions

The PHM 2012 dataset includes three operating conditions:

Condition RPM Radial Load Fr (Hz) BPFO (Hz) BPFI (Hz)
Condition 1 1800 4000 N 30.0 156.59 233.43
Condition 2 1650 4200 N 27.5 143.54 213.98
Condition 3 1500 5000 N 25.0 130.49 194.53

Parameter Modifications

1. Sampling Parameters

Parameter Original (MFP) New (PHM 2012) Description
fs 50000 Hz 25600 Hz Original sampling frequency
ts 1/50000 1/25600 Sampling period (auto-calculated)
tsa_fs 80 Hz 180 Hz TSA resampling frequency
tsa_ts 1/80 1/180 TSA sampling period (auto-calculated)

Rationale for tsa_fs = 180 Hz:

  • For a shaft frequency of 30 Hz (Condition 1), 180 Hz provides 6 samples per revolution
  • Original 80 Hz would only provide ~2.67 samples per revolution (insufficient for accurate TSA)

2. Bearing Characteristic Frequencies

Parameter Original (MFP) New (PHM 2012) Formula Description
mortor_gear 99.873 Hz 30.0 Hz Fr = RPM/60 Shaft fundamental frequency
belt_si 41.6 Hz 156.59 Hz BPFO = (Nb/2)×(1-d/D)×Fr Ball pass frequency outer
mortor 1597.97 Hz 233.43 Hz BPFI = (Nb/2)×(1+d/D)×Fr Ball pass frequency inner
high_hamonic 20673.84 Hz 466.86 Hz BPFI×2 Second harmonic

Calculation Details (Condition 1: 1800 RPM):

Given:
- Nb = 13 (rolling elements)
- D = 34 mm (pitch diameter)
- d = 6.7 mm (ball diameter)
- Fr = 1800/60 = 30 Hz (shaft frequency)

BPFO = (13/2) × (1 - 6.7/34) × 30 = 6.5 × 0.803 × 30 = 156.59 Hz
BPFI = (13/2) × (1 + 6.7/34) × 30 = 6.5 × 1.197 × 30 = 233.43 Hz
FTF  = (1/2) × (1 - 6.7/34) × 30 = 0.5 × 0.803 × 30 = 12.05 Hz
BSF  = (34/(2×6.7)) × (1 - (6.7/34)²) × 30 = 2.537 × 0.961 × 30 = 73.16 Hz

3. Frequency Range Parameters

Parameter Original (MFP) New (PHM 2012) Description
side_band_range 1.664 2.0 Sideband tolerance (±2 Hz)
harmonic_gmf_range 1.5 1.0 Harmonic tolerance
mortor_gear_range 2.5 2.0 Shaft frequency range
belt_si_range 2.5 2.0 BPFO frequency range
morotr_range 8.29 3.0 BPFI frequency range
high_hamonic_range 5 5.0 High-order harmonic range

4. STFT Parameters (Unchanged)

Parameter Value Time Resolution Frequency Resolution
stft_hann_nperseg 128 5 ms 200 Hz
stft_flattop_nperseg 256 10 ms 100 Hz
cwt_scale_max 64 - -

These parameters are optimized for 2560 points per file at 25600 Hz sampling rate.

Usage

Basic Usage

from backend.initialization import InitParameter

# Create instance with default Condition 1 (1800 RPM)
params = InitParameter()

print(f"Sampling rate: {params.fs} Hz")
print(f"Shaft frequency: {params.mortor_gear} Hz")
print(f"BPFO: {params.belt_si} Hz")
print(f"BPFI: {params.mortor} Hz")

Switching Working Conditions

# Switch to Condition 2 (1650 RPM)
info = params.set_working_condition(2)
print(info)
# Output: {'condition': 2, 'rpm': 1650, 'load_N': 4200, ...}

# Switch to Condition 3 (1500 RPM)
info = params.set_working_condition(3)
print(info)

# Get current condition info
current = params.get_current_condition_info()
print(current)

Condition-Specific Reference Frequencies

# Access pre-calculated frequencies for all conditions
print(f"Condition 1 BPFO: {params.bpfo_condition1} Hz")
print(f"Condition 2 BPFO: {params.bpfo_condition2} Hz")
print(f"Condition 3 BPFO: {params.bpfo_condition3} Hz")

# Additional frequencies (FTF, BSF)
print(f"Condition 1 FTF: {params.ftf_condition1} Hz")
print(f"Condition 1 BSF: {params.bsf_condition1} Hz")

Bearing Fault Frequencies

Fault Type Frequency Description
Inner Race BPFI Fault on inner raceway
Outer Race BPFO Fault on outer raceway
Ball/Roller BSF Fault on rolling element
Cage FTF Fault on cage/retainer

Parameter Summary Table

Category Parameter PHM 2012 Value Original MFP Value
Sampling fs 25600 50000
tsa_fs 180 80
Shaft mortor_gear 30.0 99.873
Inner Race mortor 233.43 1597.97
Outer Race belt_si 156.59 41.6
Harmonic high_hamonic 466.86 20673.84
Ranges side_band_range 2.0 1.664
harmonic_gmf_range 1.0 1.5
mortor_gear_range 2.0 2.5
belt_si_range 2.0 2.5
morotr_range 3.0 8.29

References

  1. Nectoux, P., et al. (2012). PRONOSTIA: An experimental platform for bearings accelerated degradation tests. IEEE International Conference on Prognostics and Health Management, Denver.

  2. PRONOSTIA Platform Specifications:

    • Bearing: SKF NKRF 25/20
    • Number of rolling elements: 13
    • Pitch diameter: 34 mm
    • Ball diameter: 6.7 mm

Validation

To verify the parameters:

from backend.initialization import InitParameter

# Test loading
p = InitParameter()
assert p.fs == 25600
assert p.mortor_gear == 30.0
assert p.belt_si == 156.59

# Test condition switching
info = p.set_working_condition(2)
assert p.mortor_gear == 27.5
assert p.belt_si == 143.54

print("All parameters validated successfully!")

Notes

  • All original MFP parameters are preserved as comments in the code
  • Default initialization uses Condition 1 (1800 RPM, 4000 N)
  • Use set_working_condition() to switch between conditions
  • STFT parameters remain unchanged as they are well-suited for the data format